Production of polyanhydride epoxide prepolymer compositions

ABSTRACT

Polyanhydrides are produced by a novel bulk polymerization procedure from maleic monomers and alkyl styrenes. The polyanhydrides, of low molecular weight and containing maleic monomer to alkyl styrene in a ratio greater than 1 to 1, are particularly useful as hardeners for epoxy resin-containing compositions and give rise to epoxy compositions which result in cured products exhibiting high heat distortion temperatures and excellent electrical and shelf life properties.

This is a division of application Ser. No. 345,172, filed Mar. 26, 1973now U.S. Pat. No. 3,929,738 which is a divisional of application Ser.No. 81,616, filed Oct. 16, 1970, now U.S. Pat. No. 3,732,332.

The present invention relates to a novel process for the mass or bulkpolymerization of maleic monomers with alkyl substituted vinylhydrocarbons, to novel products resulting from such a process and tonovel epoxy compositions derived therefrom. One specific aspect of thepresent invention relates to a bulk polymerization process for preparingnovel, low molecular weight polymers of a maleic monomer and vinylaromatic hydrocarbon, typically co-polymers of maleic anydride andα-methyl styrene which are particularly useful as hardeners in epoxycompositions.

There is growing interest in low molecular weight polymers of maleicmonomers. Heretofore, it has been proposed to employ various techniquesof solution, bulk and the like procedures to co-polymerize maleicmonomers and vinyl hydrocarbons such as styrene. Of the bulkpolymerization techniques it has been proposed to copolymerize styreneand maleic anhydride in a 1:1 molar ratio employing a polymerizationcatalyst wherein the reagents along with the catalyst are mixed togetherand then heated to polymerization temperatures giving rise to productsof very high viscosity and of very high molecular weights.

By far the most common mode of preparing copolymers of maleic monomersand vinyl hydrocarbon employed in the art today are solvent or solutionpolymerization processes which are relatively costly since they requireremoval of the large amounts of solvent required and in general onlypermit 10 to 50 percent utilization of kettle capacity for the actualproduct being produced.

While low molecular weight copolymers have been prepared, e.g.copolymers of a molecular weight of less than 10,000 generally withinthe range of 1500 to 2,000, the molecular weight has been subject to theeffect of controlling at least three vairables with either or all ofthem exerting adverse effects. For example, it has been widely heldheretofore that either of higher temperatures, larger amounts ofcatalyst or the selection of particular solvents such as xylene wouldresult in copolymers of molecular weights below 10,000 depending on howthese parameters were controlled.

Despite the abundant amount of work done in this area, however, therestill exists serious disadvantages which preclude successful preparationof low molecular weight products. The prior procedures have sufferedfrom the disadvantages inherent in the facts that control of thepolymerization reaction once initiated has been difficult; copolymersproduced generally have a broad molecular weight range and, in general,only high molecular weight, high viscosity products have been produced.

It is highly desirable to have low molecular weight copolymers availableto the art. It is particularly desirable that such products be preparedby a low cost bulk polymerization technique which is readily controlledand which, when repeated, gives low molecular weight products in apredictable and narrow range.

Accordingly, it is an object of this invention to provide a novelpolymerization process for preparing low molecular weight polyanhydridesderived from maleic anhydride and vinyl hydrocarbons.

It is a further object of this invention to provide a process whereinmore consistent and specific properties of the polyanhydrides areobtained.

Still another object is to provide novel, low molecular weightpolyanhydrides possessing a higher degree of reactivity, lower softeningpoints and higher molar ratios of maleic monomer.

A further object of the present invention is to provide novel epoxycompositions containing said polyanhydrides which exhibit improvedproperties.

These and other objects will be apparent from the description of theinvention which follows.

Polyanhydrides and Preparation Thereof

The above and related objects are attained by a novel process in whichthe maleic monomer is heated, preferably under an inert atmosphere, to atemperature within the range of about 160° to about 200° C. and thevinyl monomer is slowly added thereto, with agitation, at a rate whichallows for the necessary control of the heat of reaction, the reactiontemperature being maintained within said range until essentially all ofthe maleic monomer and alkyl styrene have polymerized, said reactionbeing conducted in the absence of solvent and catalyst to yield apolyanhydride having a molecular weight below about 1,000, generallywithin the range of about 200 to about 950 and especially about 300 to450, containing maleic monomer to vinyl monomer in a ratio greater than1 to 1.

The novel polyanhydrides provided by the instant process possessunusually attractive properties which render them particularly suitableas hardeners in epoxy molding compositions and offer several advantagesas hardeners over conventional mono and dianhydrides when employed insuch compositions as illustrated further hereinbelow. The novelpolyanhydrides have low softening points, e.g. 111° - 156° C., and offerbetter processibility as components of various formulated epoxycompositions suitable for use as epoxy laminating resins, epoxy pottingresins, epoxy coating resins and other miscellaneous applications wellknown to this art. Such epoxy compositions including those containingfillers show rapid cure even with epoxy resins having relatively highepoxy equivalent weight and result in cured products having high heatdistortion temperatures (HDT) and excellent electrical and shelf lifeproperties. These improvements are mainly attributed to the higher molarproportion of maleic anhydride which allows for a higher degree ofreactivity which in turn gives rise to faster cure, high HDT, etc. inepoxy resin-containing compositions.

The novel process also possesses certain advantages over priorprocedures. It is a bulk polymerization allowing virtually 100 percentutilization of kettle capacity as compared to conventional solventprocesses which utilize only 10 to 50 percent of kettle capacity foractual product produced. Secondly, elaborate and expensive equipment isnot required since any conventional polyester reaction kettle can beemployed with satisfactory results. Additionally, vacuum stripping ofthe product is not required and free vinyl monomer in the product isalways of sufficiently low concentration not to interfere with ultimateuse requirements. Under optimum conditions, for example, suchconcentrations of free vinyl monomer will be less than 1 percent.

While it is not known exactly how the instant process mechanismfunctions to produce the low molecular weight polyanhydrides or why itis successful while other attempts at bulk polymerization have not beenin achieving the same goals, it is believed that the key factors are theinstantaneous nature of the reaction at the elevated temperaturesemployed and effective control of the heat of reaction. These factorsare obtained by adding the maleic anhydride initially, adding the vinylmonomer at a slow rate and effecting the reaction at an elevatedtemperature. It is believed that the slow addition of the vinyl monomerkeeps the amount of free monomer so low that the heat of reaction iseasily dissipated and thereby prevents the normally run-away reactionand allows production of low molecular weight products. Moreover, it isbelieved that the high temperature at which the reaction is initiated isof critical importance. It is believed that at temperatures lower than160° C., initiation of the reaction is so slow as to permit a buildup ofmonomer which, once the reaction is initiated, allows for a run-away,uncontrolled reaction. To the contrary, at temperatures of from about160° C. to 200° C., the latter temperature being the reflux temperatureof maleic anhydride, reaction is spontaneous and this condition, coupledwith the slow addition of vinyl monomer permits control of the heat andrate of reaction.

The process of the invention is generally adaptable to thecopolymerization of alkyl substituted styrenes including thosecontaining additional substituents inert to the reaction. In general,such alkyl styrenes are of the formula: ##STR1## wherein R is hydrogenor alkyl containing 1 to 4 carbon atoms with the proviso that when X₁and X₂ are hydrogen, R is alkyl; X₁ and X₂ are hydrogen, halogen such aschloro, bromo, and iodo; alkoxy, alkyl and haloalkyl wherein the alkylgroups contain from 1 to 4 carbon atoms; acetyl, monocyclic aryl such asphenyl, tolyl, xylyl; aralkyl such as benzyl, phenetyl, etc. or X₁ andX₂ together with the benzene nucleus may form a fused ring. Such alkylstyrenes include α-methyl styrene, isopropyl styrene, vinyl toluene,tertiary butyl styrene, vinyl xylene, 2,4-dimethyl styrene,2-methyl-4-chlorostyrene, vinyl naphthalene, 2-methyl-4-benzyl styrene,and mixtures thereof.

It has been found that the conventional polymerization catalysts andmolecular weight regulators heretofore believed to be essential topromote free radical initiation are not necessary in the practice of theinstant invention. It has been previously believed that the molecularweight of the products would be significantly lowered when using highcatalyst concentrations. To the contrary and unexpectedly, in thepresent invention, such catalysts have little or no effect and offer noadvantage. Similarly, molecular weight regulators are not required toproduce the low molecular weight products of the invention although theymay be employed in certain instances if desired. Such molecular weightregulators include mercaptans, for example, isooctyl mercaptan,octadecyl mercaptan, lauryl mercaptan, etc. nitrostyrene,chlorohydrocarbons for example chlorobenzene, dichlorobenzene,chloroxylene, etc. and other compounds well known in the art for thispurpose.

It is a distinction of this invention that the preferred vinyl monomer,α-methyl styrene, appears to function as a molecular weight regulator inthe instant reaction. This is illustrated by preparation of extremelylow molecular weight polyanhydride copolymers, e.g. 300- 450 M.W., whenreacting α-methyl styrene and maleic anhydride. The molecular weights ofcopolymers are slightly higher when employing alkyl styrenes other thanα-methyl styrene. For example, tertiary butyl styrene-maleic anhydridecopolymer has a M.W. of about 638 while the terpolymer with α-methylstyrene has a molecular weight of about 550. Thus, the preferredpolyanhydrides of the invention will be copolymers of α-methyl styreneand maleic anhydride and terpolymers of α-methyl styrene, other alkylstyrenes, for example, tertiary butyl styrene and maleic anhydride.Alternatively, copolymers of alkyl styrenes other than α-methyl styrenebut exhibiting the lowest molecular weight may also be prepared byemploying molecular weight regulators such as lauryl mercaptan asillustrated further hereinbelow. Use of the latter molecular weightregulator is not preferred, however, since it imparts an unpleasant odorto the final product. It is a further distinction of this invention thatwhile copolymers, terpolymers, etc. of the alkyl styrenes with maleiccompounds may be prepared having low molecular weights, styrene, whichis normally the preferred reactant in other procedures, is not operableunless reacted in conjunction with one of the alkyl styrenes of theinvention. As will be illustrated further hereinbelow, attempts toproduce styrene-maleic anhydride copolymers in the absence of alkylstyrene by the present process resulted in run-away reactions with largeamounts of polystyrene forming over the sides of the reactor, theproducts being extremely viscous and having high molecular weights.

The maleic compounds copolymerized with the above vinyl monomers are, ingeneral, compounds which have one carboxyl group attached to each carbonatom of an olefinic group, i.e., wherein two carbon atoms are joined bya double bond. The remaining valences of each of the double bondedcarbon atoms are generally satisfied by organic groupings or inorganicgroupings which are essentially inert in the principal copolymerizationreaction. Thus, the maleic compound will have only one olefinic linkage.Illustrative of such maleic compounds are materials defined by thefollowing general formula: ##STR2## wherein R₁ and R₂ can be hydrogen,halogen such as chloro, bromo and iodo; aryl such as phenyl, xylyl,tolyl, etc.; aralkyl such as benzyl, phenetyl, etc., or alkyl, the alkylgroups containing 1 to 10 carbon atoms; or cycloalkyl such ascyclopentyl, cyclohexyl, etc.; X and Y can be OH, or X and Y together isO. Typical examples of such compounds include maleic anhydride, methylmaleic anhydride and materials which rearrange thereto during thereaction such as itaconic anhydride; propyl maleic anhydride,1,2-diethyl maleic anhydride, phenyl maleic anhydride, cyclohexyl maleicanhydride, benzyl maleic anhydride, chloromaleic anhydride, and maleicacid. Maleic anhydride is especially preferred.

The maleic monomer and the vinyl monomer will be employed in molarratios greater than 1.0 mole maleic monomer to 1.0 mole of vinylmonomer, preferably in the range of 1.1 to 1.0 to 2.0 to 1.0.

The processing techniques of the invention are subject to variation. Ithas been found that all of the maleic monomer may be added to the kettleand heated to the prescribed temperature or a major portion may beadded, the remainder being added after all of the vinyl monomer has beenadded. In the latter procedure, the final addition of a small amount ofmaleic monomer aids in keeping the amount of free vinyl monomer in theproduct to a minimum. It is not desirable to employ reverse addition,e.g. to add vinyl monomer to the kettle followed by slow addition ofmaleic monomer since such a procedure results in highly viscouscopolymers of molecular weights outside the desired range which are notsuitable for use in epoxy molding compounds. Since under optimumconditions, there is less than 1.0% unreacted vinyl monomer, theproducts are recovered by merely pouring into containers. Recovery,where needed, however, may be easily accomplished by vacuum strippingunreacted material by conventional means.

The following examples are set forth to illustrate more clearly theprinciple and practice of this invention. Where parts or quantities areset forth, they are parts or quantities by weight.

EXAMPLES 1 TO 7

1960 parts (20 moles) of maleic anhydride were charged to apolymerization kettle after the kettle was flushed free of air withnitrogen. The charge of maleic anhydrides was heated to 180° C. withstirring after which 1770 parts (15 moles) of alpha-methyl styrene wereadded over a 31/2 hour period. After said addition was complete, thetemperature was raised to 200° C. over 30 minutes. 250 parts (2.53moles) of additional maleic anhydride was added to the reaction zone andheated to 200° to 210° C. for one hour after which the liquid wasdropped into containers. There were recovered a solid polymer having aRing and Ball softening point of 111° C., a Gardner-Holdt viscosity ofU-V (40% resin in tetrachloroethane), a molecular weight of 350 andanhydride equivalent weight of 177.

The procedure of Example 1 was repeated except the reactants andconditions were varied as indicated with the results reported inExamples 1 to 7 in Table I which follows. In Example 2, the procedurewas the same except that all of the maleic anhydride was addedinitially.

EXAMPLES 8 TO 10

For purposes of comparison, several experiments were run and arereported in Table I also.

In comparative Example 8, the procedure of Example 1 is repeated exceptthat styrene is substituted resulting in an uncontrollable reaction withhigh formation of polystyrenes.

In comparative Example 9, a 1:1 styrene-maleic anhydride copolymer isprepared by solvent process as follows:

Part A

2400 grams xylene

Part B

2.4 moles maleic anhydride

2.4 moles styrene

11/2% tertiary butyl perbenzoate catalyst

320 grams xylene

Part A is charged to the kettle and heated to 95°-100° C. Part B isdissolved together and added to the reaction vessel over a 2 hour periodafter which it is maintained in the vessel for 2 hours at 95°-100° C.,cooled to 30° C. and filtered. The product starts to precipitate after30 minutes and is recovered as a finely divided precipitate. The productcould not be melted for softening point determination as it blackened orcarbonized as the temperature increased. The softening point was therebyindicated to be well above 200° C.

In comparative Example 10, a commercially available 1:1 styrene-maleiccopolymer, commercially available as SMA 1000-A, Arco Chemical Company,is listed and employed in subsequent experiments hereinbelow.

In Table I, abbreviations where they appear have the following meanings:αMS is alpha methyl styrene; S is styrene; VT is vinyl toluene; TBS istertiary butyl styrene; TCE is tetrachloroethane; DMF is dimethylformamide; and TBPB is tertiary butyl perbenzoate catalyst.

                                      Table I                                     __________________________________________________________________________    Example        1     2     3        4       5                                 __________________________________________________________________________    Maleic Anhydride                                                                              20   12    9.0      8       9.0                                (Moles)                                                                        A                                                                             B             2.53 --    0.6      1       0.6                               Vinyl Monomer  αMS                                                                           αMS                                                                           VT       S-6.0   TBS                               (Moles)        15.0  6     7.2      αMS-2.0                                                                         7.2                               Ratio of Reactants                                                                           1.0/1.5                                                                             1/2   1.0/1.33 1.0/1.125                                                                             1.0/1.33                          Vinyl Monomer/Maleic                                                          Monomer                                                                       Solvent        --    --    --       --      --                                Other Reactant --    --    46.5g.Lauryl                                                                           --      --                                                           Mercaptan                                          Catalyst       --    --    --       --      --                                Addition Time, Hours                                                                         31/2  2     31/2     3-3/4   31/2                              Reaction Temperature, ° C.                                                             180°                                                                        180°                                                                         180°                                                                            180°                                                                           180°                       Gardner-HoldtViscosity                                                                       U-V   U     M        W       Y                                                40% resin                                                                           40% resin                                                                           30% resin                                                                              60% resin                                                                             30% resin                                        TCE   TCE   TCE      DMF     TCE                               Molecular Weight                                                                             350   355   432      485     638                               Anhydride Equivalent                                                                         177   158   191      187     214                               Weight                                                                        Softening Point, ° C.                                                                  111°                                                                        123°                                                                         122°                                                                            140°                                                                           156°                       Remarks                                                                       Example        6     7     8        9       10                                __________________________________________________________________________    Maleic Anhydride                                                                             8     8     6.0      2.4     --                                 (Moles)                                                                        A                                                                             B            1     1     0.4      --      --                                Vinyl Monomer (Moles)                                                                        VT-6.0                                                                              TBS-6.0                                                                             S        S       S                                                αMS-2.0                                                                       αMS-2.0                                                                       4.8      2.4                                       Ratio of Reactants                                                                           1.0/.sup.- 1.125                                                                    1.0/1..sup.- 125                                                                    1.0/1.3  1.0/1.0 1/1                               Vinyl Monomer/Maleic                                                          Monomer                                                                       Solvent        --    --    --       Xylene  --                                Other Reactant --    --    --       --      --                                Catalyst       --    --    --       1.5%    --                                                                    TBPB                                      Addition Time, Hours                                                                         4     41/2  31/2     2       --                                Reaction Temperature, ° C.                                                             180°                                                                         185°                                                                         180°                                                                            95-100°                                                                       --                                Gardner-HoldtViscosity                                                                       X-Y   Y     --       --      --                                               60% resin                                                                           40% resin                                                               DMF   TCE                                                      Molecular Weight                                                                             556   555   --       --      1600                              Anhydride Equivalent                                                                         202   232   --       --      225                               Weight                                                                        Softening Point, ° C.                                                                  145°                                                                         132°                                                                        --       >200°                                                                          >200°                      Remarks                    Reaction stopped                                                                       Would not melt                                                                        Commercially                                                 after 3/4 of                                                                           for softening                                                                         available -                                                  Styrene added.                                                                         point; carbon-                                                                        SMA - 1000A.                                                 Large amounts of                                                                       ized before                                                          Polystyrenes                                                                           softening.                                                           over sides &                                                                  top of reactor.                                    __________________________________________________________________________

Polyanhydride Prepolymer

In a preferred embodiment of this invention, low melting, economicalepoxy-hardener prepolymers are provided which have extremely low Ringand Ball softening points and provide greater ease of processing withadditional epoxy resin and other components of epoxy composition. Forexample, in the preparation of epoxy molding compounds, to optimizeblending of the hardener with the resin of the molding compound when thepolyanhydrides per se are employed, the polyanhydrides are first ballmilled to a fine powder prior to blending and processing. This step isnot necessary when employing the polyanhydride prepolymer. Additionally,this embodiment of the invention permits ready use of liquid epoxyresins of low epoxy equivalent weight and high reactivity.

The preparation of the prepolymer is simple in that the epoxy resin issimply added to the polyanhydride hardener product while it is still inthe reaction kettle. The prepolymers are characterized by good stabilityand range from viscous liquids to materials which exhibit Ring and Ballsoftening points below 100° C., generally within the range of about 40°to 95° C.

A variety of low equivalent weight epoxy resins can be reacted with thepolyanhydrides to form the prepolymer herein. They include glycidylpolyethers of polyhydric alcohols and polyhydric phenols well known inthe art, for example, diglycidyl ethers of Bisphenol A commerciallyavailable as Epon resins. Other suitable resins include polyglycidylethers of phenol-formaldehyde novolacs and cresol-formaldehyde novolacs,cycloaliphatic epoxy resins, etc. In general, suitable epoxy resins willbe characterized as having an epoxy equivalent weight within the rangeof about 75 to about 500.

The prepolymers are prepared by adding from about 0.1 to about 1.3equivalents of epoxy per anhydride equivalent weight.

This aspect of the invention will be better understood from the examplewhich follows:

EXAMPLE 11

Following the procedure of Example 2 and employing the reactantsthereof, the reaction is allowed to cool to 155° C. A commerciallyavailable diglycidyl ether of Bisphenol A, having a molecular weight of380- 400 (at 45° to 50° C.) equal to 54 percent of the charge in thekettle is added over 5 to 10 minutes with stirring. The temperaturedrops to about 115° C. and is held there for 30 minutes after which theproduct is dropped into containers. The product is a prepolymercontaining 65% polyanhydride/35% epoxy, has a Ring and Ball Softeningpoint of 81° to 85° C. and a Gardner Holdt viscosity (40% resin intetrachloroethane) of D-G.

When the polyanhydride of Example 1 is substituted in the aboveexperiment, a prepolymer is received of comparable viscosity and havinga softening point within the range of 69° to 76° C.

Epoxy Molding Compounds

Epoxy molding compounds employing the polyanhydrides or prepolymers ofthis invention have improved physical and molding properties especiallyin high temperature dry and wet electrical properties of the moldedpieces, in shelf life of the molding compounds and in release duringmolding.

Suitable epoxy molding compounds may be prepared by conventionaltechniques, for example, by dry blending the components in a suitablemixer followed by suitable processing, for example, fusion on a heatedtwo roll mill. Process temperatures will vary according to the resin andhardener types employed but are generally within the range of about 75°F. to 250° F. The fused product is then cooled and granulated in asuitable grinder such as a Fitzpatrick mill.

The resulting molding compounds can be molded using conventionalprocedures and equipment familiar to those skilled in the art. It willbe understood that the temperature employed and the length of cure willvary depending on the particular resin system employed. In generaltemperatures ranging from about 140° to about 200° C. will besufficient.

The epoxy resin component of the molding compound are those containingmore than one ##STR3## group. The polyepoxides may be saturated orunsaturated, aliphatic, cycloaliphatic, heterocyclic, aromatic and maybe substituted if desired with substituents such as chlorine, hydroxyl,ether radicals and the like.

Various examples of polyepoxides that may be used in the process of theinvention are given in U.S. Pat. No. 2,633,458 and it is to beunderstood that so much of the disclosure of the patent relative toexamples of polyepoxides is incorporated by reference into thisspecification.

Other examples include the epoxidized esters of the polyethylenicallyunsaturated monocarboxylic acids such as epoxidized linseed, soybean,perilla, oiticia, tung, walnut and dehydrated castor oil, methyllinoleate, butyl linoleate, ethyl 9,12-octadecadienoate, butyl9,12,15-octadecatrienoate, butyl eleostearate, monoglycerides of tungoil fatty acids, monoglycerides of soybean oil, sunflower, rapeseed,hempseed, sardine, cottonseed oil, and the like.

Another group of the epoxy-containing materials used in the process ofthe invention include the epoxidized esters of unsaturated monohydricalcohols and polycarboxylic acids, such as, for example,di(2,3-epoxybutyl) adipate, di(2,3-epoxybutyl)oxalate,di(2,3-epoxyhexyl) succinate, di(3,4-epoxybutyl) maleate,di(2,3-epoxyoctyl) pimelate, di(2,3-epoxybutyl) phthalate,di(2,3-epoxyoctyl) tetrahydrophthalate, di(4,5-epoxydodecyl) maleate,di(2,3-epoxybutyl) terephthalate, di(2,3-epoxypentyl) thiodipropionate,di(5,6-epoxytetradecyl) diphenyldicarboxylate, di(3,4-epoxyheptyl)sulfonyldibutyrate, tri(2,3-epoxybutyl) 1,2,4-butanetricarboxylate,di(5,6-epoxypentadecyl) tartarate, di(4,5-epoxytetradecyl) maleate,di(2,3-epoxybutyl) azelate, di(3,4-epoxybutyl) citrate,di(5,6-epoxyoctyl) cyclohexane-1,2-dicarboxylate, di(4,5-epoxyoctadecyl)malonate.

Another group of the epoxy-containing materials includes thoseepoxidized esters of unsaturated alcohols and unsaturated carboxylicacids, such as 2,3-epoxybutyl 3,4-epoxypentanoate, 3,4-epoxyhexyl3,4-epoxypentanoate, 3,4-epoxycyclohexyl, 4,5-epoxyoctanoate,2,3-epoxycyclohexylmethyl epoxycyclohexane carboxylate.

Still another group of the epoxy-containing materials includedepoxidized derivatives of polyethylenically unsaturated polycarboxylicacids such as, for example, dimethyl 8,9,12,13-diepoxyeicosanedioate,dibutyl 7,8,11,12-diepoxyoctadecanedioate, dioctyl10,11-diethyl-8,9,12,13-diepoxy-eiconsanedioate, dihexyl6,7,10,11-diepoxyhexadecanedioate, didecyl9-epoxy-ethyl-10,11-epoxyoctadecanedioate, dibutyl3-butyl-3,4,5,6-diepoxycyclohexane-1,2-dicarboxylate, dicyclohexyl3,4,5,6-diepoxycyclohexane-1,2-dicarboxylate, dibenzyl1,2,4,5-diepoxycyclohexane-1,2-dicarboxylate and diethyl5,6,10,11-diepoxyoctadecyl succinate.

Still another group comprises the epoxidized polyesters obtained byreacting an unsaturated polyhydric alcohol and/or unsaturatedpolycarboxylic acid or anhydride groups, such as, for example, thepolyester obtained by reacting 8,9,12,13-eicosanedienedioic acid withethylene glycol, the polyester obtained by reacting diethylene glycolwith 2-cyclohexene-1,4-dicarboxylic acid and the like, and mixturesthereof.

Still another group comprises the epoxidized polyethylenicallyunsaturated hydrocarbons, such as epoxidized 2,2-bis(2-cyclohexenyl)propane, epoxidized vinyl cyclohexene and epoxidized dimer ofcyclopentadiene.

Another group comprises the epoxidized polymers and copolymers ofdiolefins, such as butadiene. Examples of this include, among other,butadiene-acrylonitrile copolymers (Hycar rubbers), butadiene-styrenecopolymers and the like.

Another group comprises the glycidyl containing nitrogen compounds, suchas diglycidyl aniline and di- and triglycidylamine.

The polyepoxides that are particularly preferred for use in thecompositions of the invention are the glycidyl ethers and particularlythe glycidyl ethers of polyhydric phenols and polyhydric alcohols. Theglycidyl ethers of polyhydric phenols are obtained by reactingepichlorohydrin with the desired polyhydric phenols in the presence ofalkali.

Polyether A and Polyether B described in the above-noted U.S. Pat. No.2,633,458 are good examples of polyepoxides of this type. Other examplesinclude the polyglycidyl ether of1,1,2,2-tetrakis(4-hydroxyphenol)ethane (epoxy value of 0.45 eq./100 g.and melting point 85° C.), polyglycidyl ether of1,1,5,5-tetradis(hydroxyphenol)pentane (epoxy value of 0.514 eq./100 g.)and the like and mixtures thereof. Other examples include the glycidatednovolacs obtained by reacting epichlorohydrin with novolac resinsobtained by condensation of aldehydes with polyhydric phenols.

The polyepoxide and polyanhydride hardeners are employed in proportionsto provide at least 0.5 equivalent of anhydride. Generally, theproportions will range from 0.5 to 2.0 anhydride group per epoxy groupand preferably from about 0.7 to 1.1.

Various catalysts may be employed to promote the curing of saidcompositions and are well known within this art. Such catalysts includebasic and acidic catalysts such as the metal halide Lewis acids, e.g.boron trifluoride, stannic chloride, zinc chloride and the like; theamines, e.g. alphamethyl benzyl-dimethylamine, dimethylethylamine,dimethylaminoehtylphenol, 2,4,6-tris(dimethylaminoethyl)phenol,triethylamine and the like. Such compounds are employed in the amountsconventional in the art, e.g. from about 0.1 to 5.0 percent by weight ofthe binder system.

Various other ingredients may be mixed with the polyepoxide compositionincluding pigments, dyes, mold lubricants and the like.

Fillers may be employed in the instant polyepoxide compositions invarying amounts to convey special properties thereto where desired. Suchfillers suitable for use include among others, silica, mica, calciumcarbonate, fiberglass, talc, asbestos, alumina, zinc oxide, celluloseand mixtures thereof. The amount of filler added to the polyepoxidecomposition may vary over a wide range. In general, amounts ranging fromabout 500 to 50 parts by weight per 100 parts by weight of polyepoxidecomponent are preferred.

The following examples are given to illustrate epoxy molding compoundsof this invention.

EXAMPLES 12 TO 20

Epoxy molding compounds are prepared employing 22.9 parts by weight ofdiglycidyl ether of bisphenol A, having an equivalent weight of 488, 7.1parts by weight polyanhydride hardener, 0.2 parts by weighttris(dimethylaminomethyl)phenol as catalyst, 0.2 parts by weight moldlubricant, and 67.8 parts by weight silica filler. The ingredients weredry blended followed by roll milling at 140° - 150° F. after which thefused product was cooled and granulated in a Fitzpatrick mill. Theresulting molding compounds were evaluated for flow properties and shelflife and were then transfer molded at 300° F. for five minutes,postcured for 2 hours at 135° C. Molded specimens were tested formechanical and electrical properties.

The results are reported in Table II which follows in which the sameprocedure was employed in each example except that various hardenerswere substituted, as indicated. In all instances, the proportions ofepoxy resin plus hardener equaled 30 weight percent of the compositionand the A/E ratio was maintained at 0.85.

                                      TABLE II                                    __________________________________________________________________________                                       Retention of                                                                  Flow at                                             Hardener            Initial EMMI                                                                        100° F. (Shelf                               Type and    EMMI Flow                                                                             Flow & Gel                                                                          Life)       Hot Shore "D" Hardness         Exam-                                                                             Hardener                                                                           Example                                                                             Maleic/                                                                             and Gel, 300° F                                                                Time at 350° F                                                               7 days                                                                              17 days                                                                             after cure at 325°                                                     F                              ple %    No.   Vinyl Ratio                                                                         In. Sec.                                                                              In.                                                                              Sec.                                                                             In.                                                                              %  In.                                                                              %  2 min                                                                             3 min.                                                                            4                                                                                 5                  __________________________________________________________________________                                                               min                12  7.1  αMS/MA                                                                        1.5   27.5                                                                              43  37 16 29 78 30 81 60  72  73  75                          of Ex. 1                                                             13  7.5  VT/MA 1.33  17.5                                                                              41  27 13 20 74 20 74 72  72  74  75                          of Ex. 3                                                             14  8.1  TBS/MA                                                                              1.33   7.0                                                                              36  11  7 10.5                                                                             96 10.5                                                                             96 70  74  77  77                          of Ex. 5                                                             15  7.9  VT/αMS/                                                                       1.125 11  16  14 15 12.5                                                                             89 10.5                                                                             75 76  77  77  77                          MA of                                                                         Ex. 6                                                                16  8.6  TBS/αMS                                                                       1.125 14  33  16 13 14 88 13 81 70  76  79  77                          MA of                                                                         Ex. 7                                                                17  6.4  αMS/MA                                                                        2.0   20  36  27.5                                                                             13 26 95 22.5                                                                             82 77  80  80  80                          of Ex. 2                                                             18  7.4  S/αMS/MA                                                                      1.125 14.5                                                                              21  20 10 16.5                                                                             83 15 75 70  73  75  77                          of Ex. 4                                                             19  8.0  S/MA  1.0   No Flow,                                                                              5  No                                                     of Ex. 9    No Cure    Cure                                          20  8.5  S/MA  1.0   No Flow,                                                                              No                                                        of Ex. 10   No Cure Flow,                                                                         No                                                                            Cure                                             __________________________________________________________________________

Table II is an evaluation of flow, cure, and shelf life properties ofthe instant molding compositions. EMMI flow via EMMI Spiral FlowSpecification EMMI I-66 involves the transfer molding of the materialfrom a pot through a sprue into an open ended spiral cavity undercontrolled conditions of temperature and pressure. The Gel Time reportedin Table II was determined by the use of a ram follower device inconjunction with the EMMI Spiral Flow mold.

The first observation readily apparent from the table is that bothcompounds based on solvent polymerized styrene maleic anhydride at a 1:1ratio did not cure and had little or no flow even at 350° F., a factprobably attributable to the high softening points of these compoundswhich prevent adequate fusion of the hardener with the resin which isrequired for adequate cure and flow. All of the products of the presentinvention possess good flow, cure and hardness properties and very goodshelf life, an advantage over many existing epoxy molding compounds.

The epoxy molding compounds of the above examples were similarlyevaluated for other properties such as heat distortion temperatures(HDT), flexural strength and electricals, the results of which arereported in Table III. Moisture absorption data after 16 hours at 15psig. steam was determined and reported below. Dielectric constants (DK)and dissipation factors (DF) were determined on these materials at 25°C., 175° C., and at 25° C. after exposing the test piece for 16 hours ina pressure cooker at 15 psig steam.

    __________________________________________________________________________                 HDT, ° C                                                               After cure at                 Electricals                                     325° F. for 5                                                                            % Water                                                                             DK    DK    DF       DF                               min.              Absorption                                                                          60 cycles                                                                           1 KC  60 cycles                                                                              1 KC                             Post-cure                                                                             Flexural                                                                           Flexural                                                                           16 hrs.,                                                                            (a) 25° C                                                                    (a) 25° C                                                                    (a) 25° C                                                                       (a) 25°                                                                C                         Hardener                                                                             2 hrs. at                                                                             Strength                                                                           Modulus                                                                            15 psig                                                                             (b) 175° C                                                                   (b) 175° C                                                                   (b) 175° C                                                                      (b) 175°                                                               C                   Example                                                                             Type   175° C                                                                         psi  psi × 10.sup.6                                                               Steam (c) 25° C*                                                                   (c) 25° C*                                                                   (c) 25° C*                                                                      (c) 25°      __________________________________________________________________________                                                              C                   12A   αMS/MA                                                                         153° C.                                                                        16,037                                                                             1.78  .74  (a) 4.19                                                                            (a) 3.99                                                                            (a) .0094                                                                              (a) .0089                 of Ex. 1                       (b) 5.21                                                                            (b) 4.94                                                                            (b) .0390                                                                              (b) .0252                                                (c) --                                                                              (c) 7.25                                                                            (c) --   (c) .390            13A   VT/MA  145° C.                                                                        17,646                                                                             1.83  .84  (a) 4.13                                                                            (a) 3.97                                                                            (a) .0085                                                                              (a) .0075                 of Ex. 3                       (b) 5.18                                                                            (b) 4.89                                                                            (b) .0390                                                                              (b) .0262                                                (c) 7.26                                                                            (c) 5.53                                                                            (c) .300 (c) .1242           14A   TBS/MA 148° C.                                                                        14,246                                                                             1.73  .81  (a) 4.16                                                                            (a) 4.08                                                                            (a) .0089                                                                              (a) .0075                 of Ex. 5                       (b) 5.13                                                                            (b) 4.86                                                                            (b) .0398                                                                              (b) .0139                                                (c) 11.54                                                                           (c) 6.23                                                                            (c) .742 (c) .254            15A   VT/αMS/MA                                                                      165° C.                                                                        16,269                                                                             1.87  .94  (a) 4.19                                                                            (a) 4.11                                                                            (a) .0086                                                                              (a) .0085                 of Ex. 6                       (b) 5.27                                                                            (b) 5.03                                                                            (b) .0427                                                                              (b) .0271                                                (c) 6.13                                                                            (c) 5.29                                                                            (c) .154 (c) .0695           16A   TES/αMS/MA                                                                     167° C.                                                                        15,012                                                                             2.02  .76  (a) 4.11                                                                            (a) 4.05                                                                            (a) .0086                                                                              (a) .0076                 of Ex. 7                       (b) 5.06                                                                            (b) 4.80                                                                            (b) .0354                                                                              (b) .0224                                                (c) 8.07                                                                            (c) 5.50                                                                            (c) .421 (c) .149            17A   αMS/MA                                                                         184° C.                                                                        14,360                                                                             1.75  .73  (a) 4.23                                                                            (a) 4.17                                                                            (a) .0069                                                                              (a) .0081                 of Ex. 2                       (b) 5.01                                                                            (b) 4.82                                                                            (b) .0291                                                                              (b) .0160                                                (c) --                                                                              (c) 8.49                                                                            (c) --   (c) .510            18A   MS/αMS/MA                                                                      141° C.                                                                        12,905                                                                             1.85  .96  (a) 4.22                                                                            (a) 4.16                                                                            (a) .0085                                                                              (a) .0078                 of Ex. 4                       (b) 5.37                                                                            (b) 5.09                                                                            (b) .0412                                                                              (b) .0064                                                (c) 7.00                                                                            (c) 5.70                                                                            (c) .202 (c)                 __________________________________________________________________________                                                              .0050                *After exposure to 15 psig steam for 16 hrs.                             

EXAMPLE 21

Epoxy molding compounds are prepared employing 8.0 parts by weight ofepoxy resin, a diglycidyl ether of Bisphenol A having a molecular weightof 460- 560, to which was added 13.0 parts by weight of prepolymerhardener described in Example 11, 0.14 parts by weight of tertiary aminecatalyst, 0.50 parts by weight mold lubricant and 78.3 parts by weightsilica filler.

The epoxy molding compound was evaluated for a number of moldedproperties the results of which are reported below.

    ______________________________________                                        Heat Distortion Temperature, ° C.                                                                 220                                                Flexural Strength, psi     20,000                                             Electrical Properties, Dry                                                     Dissipation Factor at                                                         60 cycles, 25° C.  .007                                                60 cycles, 175° C. .045                                               Electrical Properties, Wet                                                     (after 15 psig steam for 16 hours)                                            Weight Gain, %            0.60                                                Dissipation Factor at 60 cycles                                                                         .025                                               ______________________________________                                    

For comparative purposes, the instant molding compounds were comparedwith various monoanhydride and dianhydride cured epoxy molding compoundsand with several commercially available anhydride epoxy compounds andthe results reported in Table IV.

The formulation was as follows with variations as indicated in theTable.

    ______________________________________                                                             Wt. Percent                                              ______________________________________                                         Epoxy Resin                                                                  (diglycidylether of Bis                                                                              18.4                                                   Phenol A) Molecular                                                           Weight 1000                                                                    Hardener              9.6                                                    Tertiary Amine Accelerator                                                                           0.15                                                    Lubricants            0.6                                                     Filler                70.0                                                    Dye                   0.95                                                   ______________________________________                                    

The compounds were processed and curved as in Example 12. In the Table,cured abbreviations have the following meanings: DF is dissipationfactor; BROB means the value was so high it could not be measured by thetest employed; Commercial Epoxy Molding Compounds A, B and C arecommercially available epoxy systems containing diglycidyl ethers ofbisphenol A as resin, silica fillers and monofunctional anhydridehardeners.

    __________________________________________________________________________                                  Electricals, Wet                                Hardener              Electricals, Dry                                                                      15 psig steam                                                                            Shelf Life, 100° F.            or           A/E HDT,                                                                              DF, 60 cycles                                                                         16 hours   EMMI Flow                                                                         3  7                             Example                                                                            Epoxy System                                                                           Ratio                                                                             ° C.                                                                       25° C.                                                                     175° C.                                                                    Weight Gain                                                                          DF  Initial                                                                           days                                                                             days                          __________________________________________________________________________    22   αMS/MA                                                                           .77 135°                                                                       .0065                                                                             .100                                                                               .80   .050                                                                              30  25 22                            23   Trimellitic                                                                            1.0 121°                                                                       .017                                                                              .698                                                                               .90   BROB                                                                              31  11 --                                 Anhydride                                                                24   Phthalic 1.0 108°                                                                       .007                                                                              BROB                                                                              1.27   BROB                                                                              32  11 --                                 Anhydride                                                                25   Tetrahydro-                                                                   phthalic .90  97°                                                                       .009                                                                              BROB                                                                              1.42   BROB                                                                              51  21 --                                 Anhydride                                                                26   Hexahydro-                                                                             .90  97°                                                                       .008                                                                              BROB                                                                              1.13   BROB                                                                              50  26 --                                 phthalic                                                                      Anhydride                                                                27   Succinic 1.0  96°                                                                       .009                                                                              BROB                                                                              2.90   BROB                                                                              --  -- --                                 Anhydride                                                                28   Benzo-   1.0 172°                                                                       .007                                                                              --  1.70   BROB                                                                              26  13 --                                 phenone                                                                       Tetra-                                                                        Carboxylic                                                                    Dianhydride                                                              29   Commercial                                                                             --  128°                                                                       .007                                                                              BROB                                                                              --     BROB                                                                              39  24 18                                 Epoxy Mold-                                                                   ing Compound A                                                           30   Commercial                                                                             --   97°                                                                       .007                                                                              --  --     BROB                                                                              29  15 11                                 Epoxy Mold-                                                                   ing Compound B                                                           31   Commercial                                                                             --  112°                                                                       .007                                                                              --  --     .539                                                                              35  23 22                                 Epoxy Mold-                                                                   ing Compound C                                                           __________________________________________________________________________

It will be obvious from Table IV, that the molding compounds of theinvention are superior in all physical properties tested to thosederived from conventional monoanhydrides. Comparison to a commercialdianhydride hardener molding compound (Example 28) shows that compoundsbased on the novel anhydride hardeners are far superior in a number ofthe important properties such as shelf life and high temperature and wetelectricals. The compounds based on the novel anhydride hardener alsoexhibited superior mold release after exposure to humid agingconditions.

EXAMPLES 32 TO 36

The following examples are given to illustrate molding compounds derivedfrom other types of epoxy resins prepared by the procedure of Example12. In the Table, TBS-αMS-MA is a polyanhydride of tertiarybutylstyrene-alphamethyl styrene and maleic anhydride described in Example 7;DGEBA epoxy resins are commercially available resins of the diglycidylether of Bisphenol A type; Novolac Epoxy Resin is a polyglycidyl etherof o-cresol formaldehyde novolac; and Cycloaliphatic Epoxy Resins arelow viscosity cycloaliphatic resins,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylates.

                  Table V                                                         ______________________________________                                        Formulation     Ex. 33 Ex. 34 Ex. 35                                                                             Ex. 36                                                                              Ex. 37                               ______________________________________                                        dgeba Epoxy M.W. 700                                                                          16.5   --     --   --    --                                   DGEBA Epoxy M.W. 1000                                                                         --     12.5   --   --    --                                   Novolac Epoxy M.W. 1100                                                                       --     --     20   --    --                                   Cycloaliphatic Epoxy                                                                          --     --     --   12.5  --                                   M. W. 426                                                                     Cycloaliphatic Epoxy                                                                          --     --     --   --    11.0                                 M. W. 280                                                                     TBS-αMS-MA                                                                              8.5    8.5    14   12.5  14.0                                 Carbon Black    1.0    1.0    1.0  0.3   0.3                                  Tertiary Amine Catalyst                                                                       .13    .13    .12  .13   .13                                  Lubricant       .6     .6     .6   .6    .6                                   Silica          71.4   59.0   55.0 64.6  64.6                                 Coupling Agent  .2     .2     .2   --    --                                   Fiberglass      --     7.5    7.5  7.0   7.0                                  ZnO             1.4    1.4    1.4  --    --                                   EMMI Flow       40     30     30   31    24                                   Inches                                                                        330° F., Gel Sec.                                                                      22     22     24   18    18                                   Shelf Life, 100° F.                                                    Initial         40     30     30   31    24                                    3 days         39     25     24   13    10                                    7 days         28     22     22   --    --                                   14 days         31     --     --   --    --                                   HDT, ° C.                                                                              150°                                                                          135°                                                                          210°                                                                        200°                                                                         220°                          Dissipation Factor,                                                           60 cycles                                                                      250° C. .013   .013   .013 .017  .01                                  175° C.  .060   .082   .042 .082  .06                                  After Pressure Pot (16                                                                        .050   .050   .040 .353  .16                                  hrs., 15 psig steam)                                                          Tested at 25° C.                                                       Dielectric Constant,                                                          60 cycles                                                                      25° C.  4.20   4.36   4.18 4.06  4.06                                 175° C.  5.20   5.39   4.81 4.97  4.85                                 After Pressure Pot (16                                                                        5.22   5.30   4.78 7.61  5.55                                 hrs., 15 psig steam)                                                          Tested at 25° C.                                                       ______________________________________                                    

While the above epoxy systems have been described as particularlysuitable for use as molding compounds and this use is a preferredembodiment herein, it will be obvious to those skilled in the art thatthey are equally suitable for other uses, for example, in fusion coatingand solvent system coating laminating applications; fluid bed andelectrostatic coating applications, etc. They are further useful in suchapplications as bonding of thermal insulation wherein thermal stabilityaffords an excellent property.

The polyanhydrides can likewise be employed as coreactants with otheranhydrides, as flow promoters and elevated temperature modifiers forthermoplastics, etc.

We claim:
 1. A low molecular weight polyanhydride epoxide prepolymercomposition obtained by admixing an epoxy compound containing more than1,2-epoxy group with a polyanhydride in an amount sufficient to providefrom about 0.1 to about 1.3 equivalents of epoxy per anhydrideequivalent weight, said polyanhydride having a molecular weight belowabout 1000 and a softening point within the range of about 111° C. toabout 156° C. and being the reaction product of the mass polymerizationprocess, in the absence of a polymerization catalyst, of a maleicmonomer selected from the group consisting of maleic acid, maleicanhydride, anhydrides which rearrange to maleic anhydrides and thehalo-, aryl-, aralkyl-, alkyl-, or cycloalkyl-substituted derivativesthereof and at least one alkyl-substituted styrene in molar proportionsof said maleic monomer relative to said alkyl-substituted styrene ofgreater than 1:1, said polymerization process being effected by heatingat least a major portion of the maleic monomer to a temperature of about160° C. to about 200° C., adding the alkyl-substituted styrene to saidmaleic monomer, with agitation, at a rate which permits control of theheat of reaction and continuing the polymerization until essentially allof said maleic monomer and alkyl-substituted styrene have polymerized.2. The polyanhydride epoxide prepolymer composition of claim 1 whereinsaid epoxy resin is characterized by having an epoxide equivalent weightwithin the range of about 75 to about
 500. 3. The polyanhydride epoxideprepolymer composition of claim 1 characterized by exhibiting a Ring andBall softening point below about 100° C.
 4. The polyanhydride epoxideprepolymer composition of claim 1 wherein said epoxy compound is aglycidyl ether.
 5. The polyanhydride epoxide prepolymer composition ofclaim 1 wherein said epoxy compound is a member selected from the groupconsisting of a glycidyl polyether of a polyhydric phenol, a glycidylpolyether of a polyhydric alcohol, a polyglycidyl ether of aphenol-formaldehyde novolac, a polyglycidyl ether of acresol-formaldehyde novolac and a cycloaliphatic epoxy resin.
 6. Thepolyanhydride epoxide prepolymer composition of claim 5 wherein saidepoxy compound is a polyglycidyl ether of a polyhydric phenol.
 7. Thepolyanhydride epoxide prepolymer composition of claim 5 wherein saidepoxy compound is a polyglycidyl ether of a polyhydric alcohol.
 8. Thepolyanhydride epoxide prepolymer composition of claim 5 wherein saidepoxy compound is a polyglycidyl ether of a phenol-formaldehyde novolac.9. The polyanhydride epoxide prepolymer composition of claim 5 whereinsaid epoxy compound is a polyglycidyl ether of a cresol-formaldehydenovolac.
 10. The polyanhydride epoxide prepolymer composition of claim 5wherein said epoxy compound is a cycloaliphatic epoxy resin.
 11. Thepolyanhydride epoxide prepolymer composition of claim 5 wherein thealkyl-substituted styrene is a member selected from the group consistingof alpha-methyl styrene, vinyl toluene, tertiary butyl styrene andmixtures thereof.
 12. The polyanhydride epoxide prepolymer compositionof claim 5 wherein said maleic monomer is maleic anhydride.
 13. Thepolyanhydride epoxide prepolymer composition of claim 5 wherein saidmaleic monomer is maleic anhydride and said alkyl-substituted styrene isalpha-methyl styrene.
 14. The polyanhydride epoxide prepolymercomposition of claim 5 wherein said maleic monomer is maleic anhydrideand said alkyl-substituted styrene is tertiary butyl styrene.
 15. Thepolyanhydride epoxide prepolymer composition of claim 5 wherein saidmaleic monomer is maleic anhydride and said alkyl-substituted styrene isa mixture of alpha-methyl styrene and tertiary butyl styrene.
 16. Thepolyanhydride epoxide prepolymer composition of claim 5 wherein themaleic monomer and the alkyl-substituted styrene monomer are employed ina molar ratio of about 1.1 to 2 molar portions of maleic monomer permolar portion of alkyl-substituted styrene.
 17. The polyanhydrideepoxide prepolymer composition of claim 13 wherein said monomers areemployed in a molar ratio of about 1.5 to 2 molar portions of maleicanhydride per molar portion of alpha-methyl styrene.
 18. Thepolyanhydride epoxide prepolymer composition of claim 17 wherein saidpolyanhydride is characterized by having a softening point in the rangeof about 111° C. to 123° C. and a Gardener-Holdt viscosity at 25° C., asa 40%, by weight, solution in tetrachloroethane, not greater than aboutV.